1 Department of Building, Civil and Environmental Engineering, Concordia University, 1455 Boul de Maisonneuve Ouest, Montreal, PQ H3G 1M8, Canada; Department of Civil and Environmental Engineering, School of Engineering, Manhattan College, 3825 Corlear Ave, The Bronx, NY, 10463, United States.
2 Sherbrooke Research and Development Center, Agriculture and Agri-Food Canada, 2000 College Street, Sherbrooke, QC J1M 0C8, Canada.
3 Department of Building, Civil and Environmental Engineering, Concordia University, 1455 Boul de Maisonneuve Ouest, Montreal, PQ H3G 1M8, Canada.
4 Department of Civil, Geological and Mining Engineering, Polytechnique Montreal, H3C 3A7, QC, Canada. Electronic address: saifur.rahaman@polymtl.ca.

This study evaluated the performance of an integrated electrochemical process, which simultaneously utilizes electro-oxidation (EO) and electro-coagulation (EC) methods while removing organic and nitrogen loads from high-strength leachate obtained from anaerobic digesters. A bipolar arrangement of the aluminum electrode, sandwiched between a monopolar boron-doped diamond anode and stainless-steel cathode, integrates EC and EO into a single reactor. This arrangement demonstrated an enhancement of 33%, 27%, and 24% in removal capacity for ammonia nitrogen (AN), total Kjeldahl nitrogen (TKN), and total nitrogen, respectively, when compared to just EO at 0.8 A current intensity after 24 h. Increasing the current intensity from 0.4 A to 1.0 A enhanced the organic nitrogen and AN removal. Chemical oxygen demand (COD) exhibited initial faster removal kinetics with higher current intensities and eventually reached 95%-98% removal for intensities of 0.6 A or higher. Additional removal for AN, TKN were also observed with increasing current intensity. Lowering the pH further expedited the COD removal kinetics. Reducing and maintaining the pH at 4, 6, and 8 by dosing of hydrochloric acid (HCl) resulted in the 100% removal of AN and TKN from the integrated system in 6, 8, and 20 h, respectively. Accelerated removal of COD and the enhanced removal of AN and TKN through pH control could be linked to the formation of active chlorine species in bulk solution. The integrated system offered lower energy consumption than EO due to oxidation on the additional anodic surface of the bipolar electrode, as well as the adsorption-precipitation of contaminants in aluminum flocs.